In order to remove fluid material from a container of such material, and particularly in the event that the container of fluid material contains substantially more fluid material than is needed at any given point in time, the fluid material is typically pumped out of the container in the desired quantity. This holds true for a variety of fluid materials, including but not limited to highly viscous lubricating fluids such as high viscosity grease. However, in order to pump such materials from a container, the material must first be drawn into the pumping device. This initial drawing in of material into the pumping device is referred to by those of ordinary skill in the art as “priming” the pump. In sum, in order for a pump to effectively remove fluid from a container, the pump must first be primed. When the fluid material is highly viscous, the sheer inertia of the still fluid is substantial and such inertia must be overcome in order to prime the pump. Therefore, to prime a pump with highly viscous fluid, the priming mechanism of the pump must impart enhanced force on the fluid.
Prior art pump priming mechanisms address the problem of priming pumps with highly viscous fluid materials in a variety of ways. One such way is the creation of a partial vacuum which is then released, causing a sudden equalization of air pressure that urges the high viscosity material into the pump. As used herein, the term “partial vacuum” means an air pressure lower than an ambient air pressure.
One prior art example of the utilization of sudden release of a partial vacuum for pump priming is U.S. Pat. No. 4,249,868 to Kotyk. The Kotyk patent discloses a pump with a priming mechanism designed to address the problem of pumping high viscosity material. In the Kotyk pump, the piston travels within a cylindrical valve, which in turn travels within the pump cylinder. When the piston completes a downstroke, the cylindrical valve blocks the inlet of the pump. On the upstroke, the piston creates a partial vacuum within the cylindrical valve until the piston reaches the top of the cylindrical valve and lifts the valve such that the inlet is reopened. Upon the reopening of the inlet, the partial vacuum in the cylindrical valve is released and the sudden equalization of pressure causes the fluid material at the inlet to rush into the cylindrical valve before proceeding into the succeeding stages of the pump.
In contrast to Kotyk and other partial vacuum priming devices in the prior art, the pump priming apparatus of the present invention provides a simple piston and cylinder structure to accomplish the priming without the need for additional parts that ultimately add expense to the construction and maintenance of the pump while diminishing its reliability.